The goal of this prospective, single-arm, open-label clinical trial is to evaluate whether 18F-AGX PET imaging can be used to assess early treatment response and metabolic changes in adult patients with recurrent or residual WHO 2021 grade 2-3 IDH-mutant diffuse glioma receiving Vorasidenib therapy.

IDH-mutant diffuse gliomas often show slow tumor growth, making early treatment response difficult to evaluate using conventional structural imaging such as magnetic resonance imaging (MRI). Clinical endpoints such as progression-free survival (PFS) and overall survival (OS) typically require long follow-up periods to detect treatment effects. Therefore, the development of sensitive and noninvasive imaging methods for early evaluation of therapeutic response is needed.

This study aims to determine whether metabolic changes detected by 18F-AGX PET during Vorasidenib treatment are associated with tumor structural changes and clinical outcomes.

The main questions it aims to answer are:

• Whether early changes in tumor metabolic activity measured by 18F-AGX PET, including percentage change in maximum tumor-to-background ratio (TBRmax), are associated with changes in tumor growth rate (TGR) measured by MRI during treatment.
• Whether early metabolic response detected by 18F-AGX PET imaging after initiation of Vorasidenib treatment can predict subsequent disease progression or tumor growth dynamics.

Participants enrolled in this study will receive oral Vorasidenib once daily for 12 treatment cycles (28 days per cycle), with dosing based on body weight.

Participants will:

• Undergo baseline MRI and 18F-AGX PET imaging following surgery for recurrent or residual disease.
• Receive oral Vorasidenib continuously for 12 cycles.
• Undergo MRI scans at baseline and during treatment cycles 1, 2, 3, 6, 9, and 12 to assess structural tumor changes.
• Undergo 18F-AGX PET/CT scans at baseline and during treatment cycles 1, 2, 3, 6, and 12 to assess metabolic tumor activity.
• Provide serial blood samples for laboratory safety monitoring, including hematologic and biochemical testing.
• Undergo magnetic resonance spectroscopy (MRS) to quantify intratumoral 2-hydroxyglutarate (2-HG) levels as an indicator of IDH mutation-associated metabolic activity.

Participants will be followed for imaging-based disease progression using RANO criteria and for treatment-related adverse events during the study period.

This study will evaluate the feasibility of using 18F-AGX PET imaging as a noninvasive imaging biomarker for early response assessment in IDH-mutant diffuse glioma patients receiving targeted IDH inhibition therapy with Vorasidenib.

Diffuse gliomas harboring mutations in isocitrate dehydrogenase (IDH1 or IDH2) represent a biologically distinct subgroup of central nervous system tumors characterized by the accumulation of the oncometabolite D-2-hydroxyglutarate (2-HG). Mutant IDH enzymes catalyze the reduction of α-ketoglutarate to 2-HG, leading to widespread epigenetic dysregulation, impaired cellular differentiation, and altered tumor metabolism. These metabolic alterations are considered key drivers of glioma tumorigenesis and progression.

Vorasidenib is an oral, brain-penetrant, dual inhibitor of mutant IDH1 and IDH2 enzymes that has demonstrated clinical activity in patients with IDH-mutant diffuse glioma. By selectively inhibiting mutant IDH enzymatic activity, Vorasidenib reduces intratumoral 2-HG production and is expected to modify tumor metabolic processes. However, due to the relatively slow growth kinetics of IDH-mutant gliomas, conventional structural imaging techniques such as magnetic resonance imaging (MRI) may not detect treatment-related changes in tumor size during the early phases of therapy. As a result, reliance on morphologic imaging alone may delay the identification of therapeutic response or disease progression.

Metabolic imaging approaches have the potential to provide earlier indicators of biological treatment effects. Magnetic resonance spectroscopy (MRS) has been used to quantify intratumoral 2-HG concentrations in vivo as a surrogate of mutant IDH activity. While MRS-based measurements may reflect pharmacodynamic effects of IDH inhibition, its sensitivity and spatial resolution may limit its utility for longitudinal monitoring of treatment response in clinical practice.

Positron emission tomography (PET) imaging using radiolabeled tracers enables the quantitative assessment of tumor metabolism and has been shown to detect treatment-related metabolic changes that precede morphologic alterations observed on MRI. Amino acid PET tracers such as 18F-FET and 18F-FDOPA have demonstrated the ability to identify early metabolic responses in glioma patients undergoing systemic therapy, with metabolic response correlating with clinical outcomes in some studies.

18F-AGX is a novel PET radiotracer designed to selectively bind to IDH-mutant glioma cells. Preclinical studies have demonstrated that 18F-AGX crosses the blood-brain barrier and exhibits increased uptake in IDH-mutant glioma models compared with IDH wild-type tumors. In experimental settings, treatment with Vorasidenib has been associated with reductions in tracer uptake that parallel decreases in intratumoral 2-HG levels, suggesting that 18F-AGX PET imaging may serve as a noninvasive indicator of target engagement and metabolic response.

This clinical study is designed to evaluate the feasibility of using 18F-AGX PET imaging to monitor metabolic changes in patients with recurrent or residual IDH-mutant diffuse glioma receiving Vorasidenib therapy. Longitudinal multimodal imaging will be performed during treatment to assess temporal changes in tumor metabolic activity and structural characteristics.

PET imaging will be conducted following intravenous administration of 18F-AGX. Quantitative image analysis will be performed using tumor-to-background uptake metrics derived from standardized uptake values (SUV). Regions of interest will be defined on PET images with reference to co-registered MRI data to allow for spatial correlation between metabolic and structural tumor features.

MRI will be performed using standardized acquisition protocols to assess tumor morphology, including T2-weighted and FLAIR sequences. MR spectroscopy may be performed to quantify intratumoral 2-HG concentrations as a complementary metabolic biomarker associated with mutant IDH activity.

Serial laboratory testing will be conducted throughout the study to monitor participant safety during Vorasidenib treatment. Adverse events will be assessed according to applicable clinical research standards.

Imaging-based disease status will be evaluated using established neuro-oncology response assessment criteria. Participants may receive additional standard-of-care interventions if clinically indicated during or after completion of the treatment period.

The results of this study are intended to provide preliminary clinical data on the use of 18F-AGX PET imaging as a noninvasive method for detecting early metabolic response in IDH-mutant diffuse glioma patients undergoing targeted IDH inhibition therapy.

Inclusion Criteria:

1. Histologically or molecularly confirmed WHO 2021 grade 2 or 3 IDH1/2-mutant diffuse glioma with recurrent or residual disease
2. At least one measurable non-enhancing lesion (≥1 cm × ≥1 cm) on postoperative T2/FLAIR MRI
3. Eligible for Vorasidenib treatment
4. Age ≥18 years
5. Karnofsky Performance Status (KPS) score ≥80
6. Adequate hematologic function
7. Adequate renal function
8. Adequate hepatic function
9. Ability to provide written informed consent

Exclusion Criteria:

1. Prior treatment with radiotherapy, chemotherapy, or IDH inhibitors
2. Known contraindications to Vorasidenib
3. Contraindications to PET/CT imaging
4. Uncontrolled hyperglycemia
5. Pregnancy or breastfeeding
6. Inability to undergo repeated intravenous injections
7. Known hypersensitivity to imaging agents or study-related medications
8. Use of strong CYP1A2 inhibitors or CYP2C19 or CYP3A substrates with narrow therapeutic index
9. Any serious comorbid condition that may interfere with study participation or safety

It is currently undecided whether individual participant data (IPD) collected in this study will be made available to other researchers. Any future data sharing will be subject to approval by the institutional review board and in accordance with applicable regulatory requirements governing the use and transfer of human subject research data.

This is an open-label study. Participants, care providers, and investigators are aware of treatment assignment. Imaging-based outcome assessments are performed by an independent central review committee blinded to clinical information and treatment response.